With advancements in semiconductor integrated circuit technology, device dimensions and component spacing continues to shrink, requiring the devices to be placed in close proximity to each other. Insulative materials are widely used in semiconductor fabrication methods for forming structures to electrically isolate the various active components formed in integrated circuits. Devices that extend into a semiconductive substrate can be electrically isolated by insulative materials formed within the substrate between the components, for example, trench isolation regions. In such a technique, trenches are etched into a silicon substrate, usually by anisotropic etching, and the trenches are subsequently filled by the deposition of an oxide such as silicon dioxide (SiO2).
An oxide is often deposited by chemical vapor deposition (CVD) as a conformal layer of SiO2. In the trenches, the conformal layers of oxide are initially formed on the sidewalls and grow in size outward into the center of the trench to where the oxide layers meet. However, as device dimensions become smaller and trench widths become narrower, such techniques can result in voids formed in the oxide fill, which impair the isolation capability of the trench.
In an attempt to eliminate voids in a high aspect ratio trench feature, flowable oxides have been developed that provide good gapfill properties. One such flowable oxide that has been employed is formed by depositing trimethylsilane ((CH3)3SiH) (TMS) and ozone (O3) by CVD to fill the gap and eliminate void formation. However, the presence of residual carbon from the hydrocarbon portion of the precursor provides a high carbon content in the oxide material that causes the fill to be soft and unstable to various processes such as wet etches, resulting in device degradation.
Attempts to reduce the carbon content in the film have included changing the deposition process by altering the ozone composition, the ozone flow, the ratio of O3:TMS flowed into the chamber, and staggering the inflow of gases, for example, first flowing only TMS, then flowing only ozone gas, etc. Although, in some applications, the amount of carbon in the fill was somewhat reduced, it was not completely eliminated from the material.
It would be desirable to develop a process for eliminating residual carbon from a flowable insulative film or fill material.